As a method for producing a single crystal of silicon carbide (SiC), the solution growth method is known. In the solution growth method, an SiC seed crystal is disposed at the lower end of a seed shaft, and the lower surface (hereinafter, referred to as a “crystal growth surface”) of SiC seed crystal is brought into contact with an Si—C solution. Thereby, an SiC single crystal is grown on the crystal growth surface of SiC seed crystal that has been brought into contact with the Si—C solution. The Si—C solution is a solution in which carbon (C) is dissolved in the melt of Si or an Si alloy.
It is preferable that the surface (hereinafter, referred to as a “growth surface”) of SiC single crystal that grows on the crystal growth surface of SiC seed crystal is flat. If a difference in temperature lies within the crystal growth surface of SiC seed crystal, a region in which the SiC single crystal is liable to grow and a region in which the SiC single crystal is less liable to grow are formed within the crystal growth surface of SiC seed crystal. For this reason, unevenness is produced on the growth surface of SiC single crystal. Therefore, in order to make the growth surface of SiC single crystal flat, it is necessary to have a uniform temperature distribution within the crystal growth surface of SiC seed crystal.
Also, in recent years, it has been required to produce a larger SiC single crystal. In order to increase the size of SiC single crystal, it is necessary to make the crystal growth surface of SiC seed crystal larger. If the crystal growth surface of SiC seed crystal is made large, the difference in temperature within the crystal growth surface of SiC seed crystal becomes liable to occur. Therefore, to produce a larger SiC single crystal as well, it is necessary to have a uniform temperature distribution within the crystal growth surface of SiC seed crystal as far as possible.
Japanese Patent Application Publication No. 2008-105896 discloses a method for producing an SiC single crystal. In the method for producing an SiC single crystal described in this publication, an SiC seed crystal that is larger than the lower end surface of the seed shaft is attached to the lower end surface of the seed shaft, and the whole of the SiC seed crystal is immersed in the Si—C solution. Therefore, the difference in temperature within the crystal growth surface of SiC seed crystal is less liable to occur as compared with the case where the crystal growth surface of SiC seed crystal is brought into contact with the liquid surface of Si—C solution.
Explaining more detailedly, in the case where the crystal growth surface of SiC seed crystal is brought into contact with the liquid surface of Si—C solution, the upper surface of SiC seed crystal comes into contact with an inert gas that fills the space in a crucible holding the Si—C solution excluding a region that is in contact with the lower end surface of the seed shaft. In this case, on the upper surface of SiC seed crystal, the heat transfer condition differs from the region that is in contact with the lower end surface of the seed shaft to other regions. In particular, in the region that comes into contact with the inert gas, the heat transfer condition changes easily, for example, due to the flow of inert gas. As the result, the temperature distribution on the upper surface of SiC seed crystal is liable to be nonuniform. If the temperature distribution on the upper surface of SiC seed crystal is uniform, usually, on the crystal growth surface of SiC seed crystal, uniform temperature distribution is ensured by the contact with the Si—C solution whose temperature is controlled. On the other hand, if the temperature distribution on the upper surface of SiC seed crystal is nonuniform, the temperature distribution on the crystal growth surface of SiC seed crystal is affected. Therefore, the temperature on the crystal growth surface of SiC seed crystal undesirably becomes nonuniform.
If the whole of the SiC seed crystal is immersed in the Si—C solution as described in the above-described publication, even on the upper surface of SiC seed crystal, uniform temperature distribution is ensured by the contact with the Si—C solution whose temperature is controlled. Therefore, the difference in temperature within the crystal growth surface of SiC seed crystal becomes less liable to occur.